Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01T—SPARK GAPS; OVERVOLTAGE ARRESTERS USING SPARK GAPS; SPARKING PLUGS; CORONA DEVICES; GENERATING IONS TO BE INTRODUCED INTO NON-ENCLOSED GASES
  • H01T19/00—Devices providing for corona discharge
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03G—ELECTROGRAPHY; ELECTROPHOTOGRAPHY; MAGNETOGRAPHY
  • G03G15/00—Apparatus for electrographic processes using a charge pattern
  • G03G15/02—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices
  • G03G15/0291—Apparatus for electrographic processes using a charge pattern for laying down a uniform charge, e.g. for sensitising; Corona discharge devices corona discharge devices, e.g. wires, pointed electrodes, means for cleaning the corona discharge device

Definitions

• This invention relates to a charger for electrophoto ⁇ graphic surfaces, to a method of charging such surfaces, and to the surfaces to be charged.
• This charging may be carried out prior to the actual exposure but it is necessary to then hold the charged surface in dark conditions to avoid bleeding
• the corona was formed between a point source and a remote electrode surface, and a stream of air was blown through the corona field on to an independent area which was to be charged, the basis being that the more acceptable components of the
• corona would be diverted by the airstream to charge the surface, the surface itself not receiving a direct charge.
• One of the objects of the present invention is to provide an arrangement wherein a selected part of the corona only is available for charging a surface, a 15. further object being to achieve this in a simple manner and with reliable operation, using charging wires extending across the area to be charged and having relative motion between the wires and area to be charged.
• the two electrodes between which the corona is formed were on opposite sides of the surface being charged, and it was customary for instance to have a backing plate on which the membrane containing the surface to be charged 25. was positioned and to have on the other side a point or a series of points, usually movable to distribute the charge pattern, or a corona wire which had relative movement in relation to the surface to achieve the charging of a selected area.
• the two wire electrodes between which the charge is applied are
• the invention also uses a control 5. electrode on the side of the surface opposite to the surface being charged, which electrode is earthed or energised to control the shape of the corona.
• the arrangement causes the corona to "brush" the surface as opposed to “impinging” on the surface.
• While charging may be effected by applying steady voltage to the wires, the present invention teaches an improved technique using a pulsed supply having a higher frequency component on it with a diminishing amplitude.
• the invention avoids the intense concentrations of electrons o the photoconductor particularly if it is a zinc oxide-resin coating which can cause "holes" in the charged regions by local repulsion of like charges causing a migration resulting in "no charge"
• the "pulsed ringing" charger as we term it, reduces the production of "holes" in the charged region by preventing the build up of unnecessary concentration of electrons by presenting a polarity reversal of 25. decreasing magnitude after each major charge step.
• the invention can conveniently comprise a pair of wires mounted on suitable insulators to extend in parallel but spaced relationship above the surface to be charged, with the two wires preferably equidistant 30. from the surface but arranged adjacent to at least a control plate, and the required high voltage is then applied to the wires in such a way that they form a pair of electrodes between which the electron flow will take place.
• the corona so formed will then spread outwardly from each of the electrodes to a 5.
• somewhat larger cross-sectional dimension at a medial point between the electrodes to form an envelope the outer, or a selected part of which, can be used to contact the surface to be charged.
• the method of charging according to this invention thus comprises positioning a pair of spaced apart corona wires on one side of a planar control electrode extending generally parallel to a plane passing through
• the corona wires but spaced from the plane, applying a high voltage between the wires to cause a corona to be generated between the wires, causing the control electrode to have a potential different from that of the corona, positioning an electrophotographic
• membrane which is to be charged between the corona wires and the control electrode, and causing relative movement between the electrophotographic membrane and the corona wires in a plane parallel to the corona wires.
• the surface to be charged can conveniently be coated 30. with zinc oxide. It is found that zinc oxide particles
• __OMPI - tend to aggregate during application, and with the object of reducing the aggregates to particles of the required fineness to give a smooth and satisfactory surface for producing high resolution, ball milling 5. has been resorted to. Such ball milling was usually done in the presence of a resin which then coated the particles of zinc oxide to provide a means of attaching the particles to a surface or to have them bedded in an insulating film.
• a surface as described can be very effectively 15. charged by the method outlined and the system results in a highly effective method of producing xerographic reproductions.
• FIG. 1 is a schematic end elevation of an assembly which shows the electrode cloud and ion streams which result according to our invention
• FIG. 2 is a schematic view of a pair of corona wires positioned above a control plate and disposed within a shield, showing a membrane being charged the differential voltage between the corona and control plate being achieved by earthing the control electrode,
• FIG. 3 shows how the control plate can be energised to function regulating the flow of electrons to the surface being charged
• FIG. 4 shows the electrical current whereby 5. "ringing" charged effects is achieved
• FIG. 5 shows a variation of Fig. 3.
• the invention can of course be carried out in many 10. ways, but according to the form shown a pair of wire electrodes are spaced a required distance apart and have the necessary high voltage applied between them, and when in use these wires are mounted on a carriage to be moved over a surface which is to be charged, or 15. the surface can move with the wires remaining in position, or in some cases, using appropriate voltages and spacing distances between the two electrodes and suitably positioning the electrodes in relation to the surface, a sufficient field area is available to charge without 20. either surface having any movement.
• the wires designated 1 - 2 are associated with a control plate 3 which is spaced from the wires to form a charging gap through which the membrane 4 to be charged is passed, and this control 25.
• plate is either earthed as ' shown in Fig. 2 or has a bias applied thereto as shown in Fig. 3.
• a shield 5 is shown on the opposite side of the wires from the control plate 3 to further control the corona, but this is not always necessary 30. but is preferred.
• the wires are connected to have a high voltage applied between them so that there is a flow of electrons, shown as a dotted area 6; which extends outwardly to touch 5- the membrane 4 under control of the control electrode 3, the ion flow being generally directly between the elctrodes as indicated by the arrows 7.
• the el.e"ctronflow is uniform over the surface between the points indicated by the distance 8, both the control electrode 3 and the shield 5 extending this distance so long as at least the control plate is earthed or has a potential applied thereto.
• electrode appears to cause the electronflow to extend over the surface and it was found that without this plate the charge appears ' to concentrate at the areas 9 and 10.
• the corona generating device • 20 comprises a high-voltage transformer 14 and rectifier 15 to give either a direct current when a condenser 16 is shunted across the high voltage of the secondary of the transformer, or a pulsating current of selected polarity, and the two sides of the secondary of the 25. transformer are connected respectively to the wire electrodes 1 and 2 to generate an electron flow which includes ions, across the gap between the electrodes
• Fig. 3 shows a voltage applied to the control 5.
• a modified corona voltage generator has a pair of transformers 20 and 21 connected in push-pull and driven by a pair of transistors 22 and 23 with oscillation produced by coupling condensers 24 and 25.
• the control electrode 3 is in this case connected 20. to earth through a variable resistance 28, although a direct earth connection is found to work but lacks the control given by the variable resistance.
• the device of Fig. 5 differs from that of Fig. 4 in that whi-le the corona producing voltage of the 25. transformers 20 and 21 is applied between the corona wires 1 and 2, and the control plate 3 is connected to the potentiometer 29 which has a voltage applied across it by a battery 30, one side of the battery 30 and the pentiometer 29 being connected to earth.
• the shield 5 can be connected to earth or to the control electrode 3.
• the assembly of Fig. 1 can be mounted on a movable frame or they could form part of a belt so that they can be driven across the surface in a continuous manner but whatever system is used it will be realised that the electrodes will be on one side only of the
• the charge can have a predetermined . ⁇ and constant configuration which will avoid puncturing
• the actual corona can be formed in various ways and can be a simple high voltage which in practice contains
• the corona can still be a pulsed corona, the corona frequency, or the frequency on a carrier of 5.
• the corona can be selected to be more effective with certain particles on or in the surface which is being charged, and it will then be possible to match the frequency of the corona to the frequency of selected particles on the surface being charged.
• these selective components can be differentially charged according to their charge acceptance when the charge is of a certain frequency or contains a band of different frequencies.
• the corona is now generated to be substantially parallel to the surface to extend over the surface, in contact with the surface, so that 5.
• the envelope of the corona can be used to charge the surface by a "brushing" action as opposed to a “bombarding” action.
• the ringing produced by the high voltage coils 20 and 21 is in 10. the higher frequency range, and it is found that this reduces the effective intensity of charge by the polarity reversals which offer an escape path for surplus electrons.
• the normal intense charge gives a saturation 15. condition whereas the "pulsed ringing" charger does not saturate, enabling a lesser exposure time, as the unsaturated ZnO coating allows easier bleeding away of the charge, particularly if used on a membrane coated with a layer of photosensitive zinc oxide applied to 20.
• the membrane as a thin layer by suspending the zinc- oxide particles in a volatile insulating, liquid having dissolved in it an insulating bonding resin, and coating the said particles with a film of liquid by bar-milling them in the liquid to -resin coat the particles in the 25. liquid before coating the membrane with the resin wetted zinc oxide particles and allowing the solvent liquid for the resin to evaporate.

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• 1981
  • 1981-05-12 JP JP50153681A patent/JPS57500624A/ja active Pending
  • 1981-05-12 EP EP19810901211 patent/EP0051624A4/de not_active Ceased
  • 1981-05-12 WO PCT/AU1981/000056 patent/WO1981003387A1/en not_active Application Discontinuation

Patent Citations (4)

Non-Patent Citations (1)

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